He supposes it starts on a random Monday morning. He’s brushing his teeth when Tommy gets out of the shower. He watches with undisguised appreciation as Tommy towels himself off efficiently, scrubs at his head with a towel and wrapping that towel around his waist as he drops a sweet kiss to Buck’s cheek. Buck spits and sits back to watch as Tommy takes the hairdryer to his hair and when he’s done, Buck notices just a few more grays on his temple. He can’t help himself, and reaches over to touch a fingertip to the spot.

Or: Buck notices Tommy’s hair is getting grayer and he loves it.